Partially metallized film having barrier properties

ABSTRACT

A partially metallized packaging film and method of making is disclosed. In one aspect, at least one portion of a vaporized metal stream is shielded from contacting a sheet of packaging film during the metallization process. The shield is a rigid plate and can be shaped to provide a sharp transition from transparent film to opaque film, or it can provide a gradual transition from transparent film to opaque film. The partially metallized packaging film can be used with a form, fill and seal machine or other packaging machine to create a food package with a product viewing window. In one aspect, the barrier web comprises a bio-based film.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional patent application of co-pending U.S.patent application Ser. No. 12/207,010 entitled “Partially MetallizedFilm Having Barrier Properties” filed Sep. 9, 2008, the technicaldisclosure of which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to customizable, metallized, flexiblepackaging material that can be used to balance product visibility withbarrier protection in packaged food products and a method of making thecustomized packaging material.

2. Description of Related Art

Multi-layered flexible film structures made from polymers are often usedin flexible packages where there is a need for its advantageous barrier,sealant, and graphics-capability properties. Barrier properties in oneor more layers are important in order to protect the product inside thepackage from light, oxygen or moisture. Such a need exists, for example,for the protection of foodstuffs, which may run the risk of flavor loss,staling, or spoilage if insufficient barrier properties are present toprevent transmission of such things as light, oxygen, or moisture intothe package.

In addition, barrier properties also prevent undesirable leaching of theproduct to the outside of the bag. For example, oily foods such aspotato chips have the potential for some oil to leach out into the filmof the bag. The sealant properties are important in order to enable theflexible package to form an airtight or hermetic seal. Without ahermetic seal, any barrier properties provided by the film areineffective against oxygen, moisture, or aroma transmission between theproduct in the package and the outside.

A graphics capability is needed because it enables a consumer to quicklyidentify the product that he or she is seeking to purchase, allows foodproduct manufacturers a way to label the nutritional content of thepackaged food, and enables pricing information, such as bar codes to beplaced on the product. At the same time, consumers also desire toactually view some products, such as potato chips or tortilla chips,through the packaging film in order generally inspect the food products'physical condition and ensure that most of the product has not beenbroken into small pieces during transport and handling.

One prior art packaging film used for packaging potato chips and likeproducts is metallized film. Metallized film is typically a polymerfilm, such as oriented polypropylene (OPP) or polyethylene terephthalate(PET), coated with a thin layer of metal. The thin layer of metal istypically applied using a physical vapor deposition process whereby themetal used for the coating is vaporized and deposited onto a sheet ofpolymer film, all under vacuum conditions. Prior art metallized film hasa shiny, opaque appearance and excellent barrier properties againstmoisture and oxygen transmission.

FIG. 1 depicts a simplified representation of a prior art apparatus forcreating metallized film. Inside a vacuum chamber 100, unmetallizedpolymer film 202 is disposed on a first roll 208 on one side of thevacuum chamber 100. The unmetallized film 202 is unrolled from the firstroll 208, travels through a vapor deposition apparatus 206 where itbecomes metallized film 204. As stated previously, the vaporized metal200 is deposited onto one surface of the film. During the process, thefilm is continuously unrolled from the first roll 208 and rolled onto asecond roll 210 disposed on the side of the vapor deposition apparatus206 opposite the first roll 208. At the conclusion of the process, thesecond roll 210 will contain a roll of metallized film 204, while thefirst roll will be empty.

While metallized film provides food packagers with a relativelyinexpensive barrier layer, as mentioned previously, the barrier isopaque. This property can be problematic when used for packages ofbreakable foodstuffs, such as potato chips or tortilla chips. Whenshopping for such breakable foodstuffs, some consumers may want to viewthe contents of the food package before actually purchasing the foodpackage to make sure its contents have not been broken to an undesirabledegree. Even for non-breakable foodstuffs, consumers may still want toinspect the contents of a food package before deciding whether topurchase it. Particularly colorful or delicious looking foods may evenentice a consumer to purchase them if viewed by the consumer. It wouldbe desirable, therefore, to provide a metallized food packaging filmwith a viewing window through which the contents of the food package canbe viewed.

As described in U.S. Pat. No. 5,530,231, a pattern of oil can bedeposited on the polymer film before the vaporized metal is deposited onthe film to prevent the deposition of metal on the film in the areasmasked by the oil. This masking oil pattern can then be washed off toreveal unmetallized portions of the film underneath. This method suffersfrom several disadvantages, including substantial increases inprocessing time and capital expense. Furthermore, this method does notprovide any way to control the degree of metallization that occurs ondifferent portions of the film. In other words, a particular portion offilm metallized using this method will be either fully metallized orcompletely unmetallized.

A need exists, therefore, to finely control the degree of metallizationover the entire surface of the film, and to do so economically.

SUMMARY OF THE INVENTION

The present invention is directed towards a metallized packaging filmhaving variable barrier properties. In one aspect, the packaging film ofthe present invention is partially metallized such that when the film isused on a form-fill-seal packaging machine, a clear product window isprovided to the consumer. In another aspect of one embodiment, thepackaging film gradually transitions from at least one opaque,metallized area to at least one transparent, non-metallized area. Inanother embodiment, the product viewing window is not transparent, butis translucent. In still another aspect of the invention, the metallizedand non-metallized areas are provided such that product logos andgraphics are not obscured. The present invention thereby provides apartially metallized packaging film with barrier properties thatapproximate fully metallized packaging films. The above as well asadditional features and advantages of the present invention will becomeapparent in the following written detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are setforth in the appended claims. The invention itself, however, as well asa preferred mode of use, further objectives and advantages thereof, willbe best understood by reference to the following detailed description ofillustrative embodiments when read in conjunction with the accompanyingdrawings, wherein:

FIG. 1 depicts a perspective view of a prior art apparatus used to makemetallized polymer film;

FIG. 2 is a cross-sectional view of prior art multi-layered packagingfilm;

FIG. 3 depicts a schematic view of a prior art apparatus used to makemulti-layered packaging film;

FIG. 4 depicts a vertical form, fill, and seal machine that is known inthe prior art;

FIG. 5 depicts an apparatus used to make the partially metallized filmof the present invention;

FIG. 6 depicts one embodiment of the vapor shield of the presentinvention; and

FIG. 7 depicts one embodiment of the partially metallized film of thepresent invention;

FIG. 8 depicts one embodiment of the food product of the presentinvention having a transparent product viewing window;

FIG. 9 depicts one embodiment of the vapor shield of the presentinvention;

FIG. 10 depicts one embodiment of the partially metallized film of thepresent invention;

FIG. 11 depicts one embodiment of the vapor shield of the presentinvention;

FIG. 12 depicts one embodiment of the vapor shield of the presentinvention;

FIG. 13A depicts one embodiment of the vapor shield of the presentinvention;

FIG. 13B depicts one embodiment of the vapor shield of the presentinvention;

FIG. 14 depicts one embodiment of the vapor shield of the presentinvention;

FIG. 14A depicts one embodiment of the vapor shield of the presentinvention;

FIG. 14B depicts one embodiment of the vapor shield of the presentinvention;

FIG. 14C depicts one embodiment of the vapor shield of the presentinvention;

FIG. 15 depicts one embodiment of the partially metallized film of thepresent invention;

FIG. 16 depicts one embodiment of the partially metallized film of thepresent invention;

FIG. 17A depicts one embodiment of the vapor shield of the presentinvention in a first position;

FIG. 17B depicts one embodiment of the vapor shield of the presentinvention in a second position;

FIG. 18A depicts one embodiment of the vapor shield of the presentinvention;

FIG. 18B depicts one embodiment of the vapor shield of the presentinvention in a first position;

FIG. 18C depicts one embodiment of the vapor shield of the presentinvention in a second position; and

FIG. 19 is a cross sectional view of one embodiment of the packagingfilm of the present invention.

DETAILED DESCRIPTION

One embodiment of the present invention is directed towards an apparatusand a method of making a partially metallized packaging film that can beused on a vertical form, fill and seal machine to create a productpackage with a viewing window. As used herein, the terms “fullymetallized packaging film” or “metallized film” mean a polymer film withat least one surface that has been coated with a thin metal layer usinga vapor deposition process or similar process known in the art. The mostcommon metal used to coat metallized film is aluminum, but other metalssuch as nickel or chromium can also be used. The typical thickness ofthe metal layer on metallized film is approximately 0.5 microns.Metallized PET film can provide about 30 times the moisture barrier andabout 400 times the oxygen barrier of a non-metallized PET film. Othermetallized polymer films provide similar gains in barrier properties.Metallized film also provides its barrier properties at a unit cost farbelow the unit cost for clear films that provide similar barrierproperties.

Metallized films are virtually opaque to visible light and UV light.While this property may be desirable from a product preservationperspective, it may not be desirable from a consumer perspectivedepending on the types of foodstuffs inside the package.

One prior art multi-layer or composite metallized film used forpackaging foodstuffs and like products is illustrated in FIG. 2 which isa schematic of a cross section of a multi-layer film 500 illustratingeach individual substantive layer. Each of these layers functions insome way to provide the needed barrier, sealant, and graphics capabilityproperties. For example, the graphics layer 114 is typically used forthe presentation of graphics that can be reverse-printed and viewedthrough a transparent outer base layer 112. Like numerals are usedthroughout this description to describe similar or identical parts,unless otherwise indicated. The outer base layer 112 is typicallyoriented polypropylene (“OPP”) or polyethylene terephthalate (“PET”). Ametal layer 120, as described above, is disposed upon an inner baselayer 118 to provide barrier properties. A sealant layer 119 disposedupon the inner base layer 118 enables a hermetic seal to be formed at atemperature lower than the melt temperature of the inner base layer. Alower melting point sealant layer 119 is desirable because melting ametallized OPP to form a seal could have an adverse effect on thebarrier properties. Typical prior art sealant layers 119 include anethylene-propylene co-polymer and an ethylene-propylene-butene-1ter-polymer. A glue or laminate layer 115, typically a polyethyleneextrusion, is required to adhere the outer base layer 112 with theinner, product-side base layer 118. Thus, at least two base layers ofpolymer film are typically required in a composite or multi-layeredfilm.

FIG. 3 demonstrates schematically the formation of material, in whichthe outer base layer 112 and metallized inner base layer 118 of thepackaging material are separately manufactured, then formed into thefinal material 500 on an extrusion laminator 400. The outer base layer112 having graphics 114 previously applied by a known graphicsapplication method such as flexographic or rotogravure is fed from roll212 while metallized inner base layer 118 is fed from roll 218. At thesame time, resin for the laminate layer 115 is fed into hopper 215 a andthrough extruder 215 b, where it will be heated and extruded at die 215c as molten polymer laminate 115. This molten polymer laminate 115 isextruded at a rate that is congruent with the rate at which the baselayer materials 112, 118 are fed, becoming sandwiched between these twolayers. The layered material 500 then runs between chill drum 220 andnip roller 230, ensuring that it forms an even layer as it is cooled.The pressure between the laminator rollers is generally in the range of0.5 to 5 pounds per linear inch across the width of the material. Thelarge chill drum 220 is made of stainless steel and is cooled to about50-60° F., so that while the material is cooled quickly, no condensationis allowed to form. The smaller nip roller 230 is generally formed ofrubber or other resilient material. Note that the layered material 500remains in contact with the chill drum 220 for a period of time after ithas passed through the rollers, to allow time for the resin to coolsufficiently. The material can then be wound into rolls (notspecifically shown) for transport to the location where it will be usedin packaging.

Once the material is formed and cut into desired widths, it can beloaded into a vertical form, fill, and seal machine to be used inpackaging the many products that are packaged using this method. FIG. 4shows an exemplary vertical form, fill, and seal machine that can beused to package snack foods, such as snack chips. This drawing issimplified, and does not show the cabinet and support structures thattypically surround such a machine, but it demonstrates the generalworkings of the machine. Packaging film 500 is taken from a roll 512 offilm and passed through tensioners 514 that keep it taut. The film thenpasses over a former 516, which directs the film as it forms a verticaltube around a product delivery cylinder 518. This product deliverycylinder 518 normally has either a round or a somewhat ovalcross-section. As the tube of packaging material is pulled downward bydrive belts 520, the edges of the film are sealed along its length by avertical sealer 522, forming a back seal 524. The machine then applies apair of heat-sealing jaws 526 against the tube to form a transverse seal528. This transverse seal 528 acts as the top seal on the bag 530 belowthe sealing jaws 526 and the bottom seal on the bag 532 being filled andformed above the jaws 526. After the transverse seal 528 has beenformed, a cut is made across the sealed area to separate the finishedbag 530 below the seal 528 from the partially completed bag 532 abovethe seal. The film tube is then pushed downward to draw out anotherpackage length. Before the sealing jaws form each transverse seal, theproduct to be packaged is metered through the product delivery cylinder518 and is held within the tube above the transverse seal 528.

The present invention is thus directed towards a method for making apartially metallized packaging film base layer, and the packaging filmitself, that can be used in conjunction with a co-extrusion machine tocreate a multi-layered partially metallized packaging film which in turncan be used with a vertical form, fill and seal machine to create ametallized product package with a product viewing window. In oneembodiment, at least one metallized target shape in the form of a logoor graphic can be included on the packaging film.

As used herein, the term “partially metallized packaging film” means apolymer film with at least one surface that has at least one area fullycoated with a thin metal layer and at least one area that is either notcoated with a thin metal layer or that is partially coated with a thinmetal layer. FIG. 5 is a representative depiction of one embodiment ofthe apparatus of the present invention used to create the partiallymetallized film of the present invention. As shown therein, inside avacuum chamber 100, unmetallized polymer film 202 is disposed on a firstroll 208 on one side of the vacuum chamber 100. The unmetallized film202 is unrolled from the first roll 208, travels through a vapordeposition apparatus 206 where it becomes partially metallized. Insidethe vapor deposition apparatus 206, the vaporized metal stream 200 issprayed towards one surface of the film. A vapor shield 300 is disposedbetween the vaporized metal stream 200 and the surface of the film to bemetallized. The vapor shield 300 blocks at least one portion of thevaporized metal stream 200 from reaching the film surface, therebyleaving at least one area of the film unmetallized or partiallymetallized. During the process, the film is continuously unrolled fromthe first roll 208 and rolled onto a second roll 210 disposed on theside of the vapor deposition apparatus 206 opposite the first roll 208.At the conclusion of the process, the second roll 210 will contain aroll of partially metallized film 220, while the first roll will beempty.

FIG. 6 depicts one embodiment of the vapor shield 300 of the presentinvention. In this embodiment, the vapor shield of the present inventionis a single plate comprising a top surface 302 and a bottom surface 204,a width 306, a length 308, and a thickness. As depicted in FIG. 5(although the specific shield depicted therein is the embodiment of FIG.9), during the metallization process the shield 300 is disposed in anapproximately co-planar arrangement with the film being metallized, butwithout touching or contacting the film. The shield is also arrangedsuch that the length 308 of the shield is approximately parallel to thefilm's direction of travel and the width 306 of the shield is parallelto the width of the film sheet. The embodiment depicted in FIG. 5 issimplified and does not depict the support structures which woulddispose the shield inside the metallization apparatus in a coplanarrelationship with the film sheet. Such support structures would be knownto one skilled in the art.

The shield embodiment depicted in FIG. 6 is the most basic embodiment ofthe present invention. It has a constant width 306 throughout its length308, and its length 308 is long enough to shield the entire portion offilm behind the shield 300 from being metallized inside themetallization apparatus 206.

FIG. 7 depicts a perspective view of a partially metallized film 220created using the shield embodiment of FIG. 6. When initiallytransparent polymer film 202 is used with this embodiment of the shield300, the resulting partially metallized film 220 comprises a strip oftransparent film 234 (or fully unmetallized film) disposed between twostrips of opaque film 230 (or fully metallized film). This embodiment isnot a preferred embodiment because the transition from the transparentfilm strip 234 to the opaque film strips 230 in this embodiment is asharp one. The sharp transition is not preferred because, ultimately,the partially metallized film 220 will be combined with an outer baselayer that has graphics and/or logos printed on it. When the sharptransition from opaque to transparent film is present in the partiallymetallized film layer 220, a distinct line corresponding to thetransition can be discerned through the graphics layer, especially wherelight pigments are used in the graphics layer. Therefore, some graphicscan be obscured or made less attractive due to the presence of thisdistinct line. An example of a product bag 600 with a distinct line isshown in FIG. 8. The preferred embodiments described below overcome thisproblem by providing a gradual transition from opaque to transparentfilm. The gradual transition region is less distinct, if not completelyinvisible, through most graphics and logo prints.

FIG. 9 depicts another embodiment of the vapor shield of the presentinvention. The FIG. 9 embodiment is shown in use in FIG. 5. FIG. 10depicts a perspective view of a partially metallized film sheet madeusing the shield embodiment of FIG. 9. As can be seen therein, itcomprises a transparent strip 234, which is bordered on both sides by atranslucent strip 232, each of which are bordered by an opaque strip230. In this embodiment, as depicted in FIG. 9, the shield comprises asingle plate with a top surface 302, a bottom surface 304, a length 308,major width 314 and a minor width 312. The major width is found at oneend of the plate and the minor width is found at the opposite end. Theresulting cross section of the plate when viewed looking directly at thetop or bottom surface 302, 304 is that of an isosceles trapezoid, withthe transition between the major and minor widths being approximatelylinear. In one embodiment, the length 308 of the vapor shield is suchthat when an initially transparent polymer film sheet undergoesmetallization, it has the following characteristics, as depicted in FIG.10: (a) one strip of the film sheet having a width 222 approximatelyequal to the minor width 312 of the shield receives no vaporized metal,and as such is a transparent film strip 234; (b) two strips of the filmsheet, one on either side of the transparent film strip 234, each ofwhich, having reduced exposure time to the vaporized metal stream 200,is partially metallized, and thereby a translucent strip 232, with eachtranslucent strip 232 having a width 224 approximately equal to half thedifference between the shield's major width 314 and minor width 312, aninner edge adjacent to said transparent film strip 234, and an outeredge opposite said transparent film strip 234; and (c) two strips of thefilm sheet that are fully metallized, or opaque film strips 230, with aninner edge adjacent to said translucent film strip 232, an outer edgecoterminous with one edge of said film sheet and a width 226 equal tothe distance between said inner and outer edges.

It will be appreciated by one skilled in the art, in view of theteachings herein, that the shield can be disposed relative to the filmsheet such that the transparent, translucent, and opaque film strips canbe located at different places laterally along the width of the filmsheet. For example, in one embodiment, the shield can be disposed withone edge coterminous with an edge of the film sheet. In this embodiment,either a translucent film strip or a transparent film strip willcomprise one edge adjacent to the film strip edge. Different embodimentsof the shield can be used in this way to provide a variety of differentpartially metallized packaging films. All embodiments of the partiallymetallized film sheets produced by this invention, regardless of wherethe particular strips are located, will comprise at least one opaquefilm strip, and at least one of a transparent film strip or atranslucent film strip.

Referring back to FIG. 10, the degree of metallization of thetranslucent film strip 232 gradually varies from almost fullyunmetallized at its inner edge to almost fully metallized at its outeredge. Thus, the transition from the opaque film strip 230 to thetransparent film strip 234 is a gradual transition. This gradualtransition from opaque to transparent is one of the novel features ofthe partially metallized film of the present invention. The opaquestrips of the film 230 provide excellent oxygen and moisture barrierproperties.

The term opaque, as used herein, means a degree of transmittance of lessthan about 5% of incident visible light. In other words, an opaque film230 allows less than about 5% of incident visible light pass through.The translucent strips 232 provide improved oxygen and moisture barrierproperties. The term translucent, as used herein to describe aparticular polymer based film, means a degree of transmittance betweenabout 5% and the degree of transmittance for that particular film in itsnon-metallized condition. In other words, a translucent film allows morethan about 5% of incident visible light to pass through, but less thanthe percentage of visible light that would pass through the sameparticular film in its non-metallized condition. The transparent stripof film 234 provides the same barrier properties as the unmetallizedpolymer film. The term transparent, as used herein to describe aparticular polymer based film, means the degree of transmittance ofincident visible light for that particular film when it is in acompletely non-metallized condition. In other words, a transparent filmis a film that allows approximately as much incident visible light topass through it as that particular film would in a completelynon-metallized condition. The term “degree of transmittance” as usedherein, when used to describe a film, means the percentage of incidentvisible light allowed to pass through the film. When a food package ismade utilizing the partially metallized film of this embodiment ofpresent invention, it has excellent barrier properties, along with atransparent product viewing window.

In the embodiment of the shield depicted in FIG. 9, the widths of thetransparent strip 234, the translucent strips 232, and the opaque strips230, as well as the degree of gradation of the translucent strips 232,can all be controlled by varying the major 314 and minor 312 widths ofthe shield. The width of the transparent strip 222 is approximatelyequal to the minor width 312 of the shield. When the shield 300 issymmetrical around its lengthwise axis, the width of each translucentstrip 224 is approximately equal to half the difference between themajor 314 and minor 312 widths of the shield. Furthermore, the rate ofchange in the degree of transmittance across the width of eachtranslucent strip 224 can be controlled by controlling the differencebetween the major 314 and minor 312 widths of the shield 300. Thegreater the difference between the major and minor widths of the shield,the more gradual the transition from the opaque strip to the transparentstrip. However, in this embodiment, the degree of control a practitionerhas over the transition region is restricted to some extent in that theamount of metal deposited onto the translucent film strip variesapproximately linearly across its width due to the trapezoidal shape ofthe shield plate. The width of each opaque strip 226 is approximatelyequal to the distance between an outer edge of each translucent strip232 and the edge of the film sheet closest in proximity to said outeredge of said translucent strip 232.

In another embodiment of the shield depicted in FIG. 9, the major width314 of the shield is made greater than or equal to the width of the filmsheet. In this embodiment, no opaque strips 230 are formed during themetallization process. A transparent strip 222 will be formed, againwith a width approximately equal to the minor width 312 of the shield.Two translucent strips 232 will be formed on opposite sides of saidtransparent strip 222. In this embodiment, the width of each translucentstrip 224 is equal to the distance between one edge of the transparentstrip 222 and the edge of the film sheet 220 closest in proximity tosaid transparent strip 222 edge. The degree of transmittance willgradually vary from almost transparent at the translucent strip edgeadjacent to said transparent strip, to almost opaque at the edge of thefilm sheet.

In FIG. 11 is depicted another embodiment of the vapor shield of thepresent invention. In this embodiment, the vapor shield comprises asingle plate with a length, a major width and a minor width. The platein this embodiment has a plurality of saw teeth 330 along its length.Preferably, in one embodiment all of the saw teeth 330 protrude from theplate to approximately equal distances. In another embodiment, depictedin FIG. 12, the saw teeth protrude from the plate at varying distances.In one embodiment, referring back to FIG. 11, the major width of theshield comprises the distance from the tips of the saw teeth on one sideof the shield to the tips of the saw teeth on the opposite side of theshield, the minor width of the shield comprises the distance from thebase of the saw teeth on one side of the shield to the base of the sawteeth on the opposite side of the shield, and the transition between itsmajor and minor widths is a saw tooth transition. As with the embodimentdepicted in FIG. 9, a film sheet metallized behind this shield will besimilar to the film strip depicted in FIG. 10, and will comprise atransparent strip 234, two graduated translucent strips 232, and twoopaque strips 230. The width of the translucent strip 224 isapproximately equal to the height of the saw teeth 332. Higher saw teethalso provide a more gradual transition from transparent to opaque. Inthis embodiment, the degree of metallization in the translucent stripagain varies approximately linearly across its width due to the linearshape of the saw tooth edges.

FIGS. 13A and 13B depict two variations of another embodiment of thevapor shield of the present invention. This embodiment is a single platewith edges that curve convexly, as in FIG. 13B, or concavely, as in FIG.13A, within the plate's major plane, along the entire length 308 of theplate. The longest width, or major width 314, of this embodiment isfound at one end, while the minor width 312, or shortest width, is foundat the opposite end, and the transition between its major and minorwidths is convex or concave, respectively. The widths of thetransparent, translucent, and opaque film strips created using thisembodiment of the vapor shield will again be defined by the major 314and minor 312 widths of the shield, and the width of the film sheet.However, the curved edges allow a practitioner of the present inventionto more finely control the variability of the metallization within thetranslucent strip because the width of the plate does not vary linearlyalong its length. Using the convex arrangement depicted in FIG. 13B, thetransition from opaque film to transparent film across the width of thetranslucent strip begins by gradually allowing more visible lightthrough nearer the outer edge of the translucent strip and thenaccelerates the rate of increase in the degree of transmittance towardsthe inner edge of the translucent strip. The concave arrangementdepicted in FIG. 13A does the opposite; the transition from the opaquefilm to the transparent film across the width of the translucent stripbegins at the outer edge of the translucent strip as a more severetransition and then decelerates the rate of increase in the degree oftransmittance towards the inner edge of the translucent strip.

FIG. 14 depicts another embodiment of the vapor shield of the presentinvention. This embodiment of the shield 300 comprises a single platewith a length 308, a major width 314, a minor width 312, and at leastone stepped change, or transition, in width 340 between said major width314 and said minor width 312. The widths of the transparent,translucent, and opaque film strips created using this embodiment of thevapor shield will again be defined by the major and minor widths of theshield, and the width of the film sheet. However, the degree oftransmittance in the translucent strip will undergo at least one stepchange which corresponds to the at least one step change 340 in thewidth of the shield. This embodiment gives practitioners of the presentinvention an alternative way of controlling the transition from opaquefilm to transparent film.

FIGS. 14A through 14C depict other embodiments of the vapor shield ofthe present invention. Each of these embodiments comprise a single platewith a length 388 and a width 306 that remains constant throughout itslength 388. These embodiments, when considered in comparison to eachother and FIG. 6, demonstrate that these embodiments of the shield havevarying lengths 388 that are shorter than the shield length 308 depictedin FIG. 6. Whereas the length 308 of the shield in FIG. 6 is long enoughto completely shield the strip of film below it from receiving any metalduring the metallization process (thus making it transparent), theshorter length 388 shields of FIGS. 14A through 14C are short enoughallow the area of film underneath to receive some metal during themetallization process, but prevent it from becoming fully metallized,thereby making the strip of film directly underneath the shieldtranslucent. Furthermore, as the length of the shield 388 is shortenedin these embodiments, the degree of transmittance for the translucentstrip directly underneath the shield will decrease. An example of asheet of partially metallized film using an embodiment of the shieldsdepicted in FIGS. 14A through 14C is depicted in FIG. 15, and has thefollowing characteristics: (a) one translucent strip 236 with a width228 equal to the width 306 of the shield; and (b) two opaque strips,each having a width 226 corresponding to the length between an outeredge of the translucent strip 236 and the corresponding edge of the filmsheet.

Other embodiments of the present invention are possible by varying thelength of the embodiments of the vapor shields depicted in FIGS. 9, 11,12, 13A and 13B. In a similar manner to that described with reference toFIGS. 14A through 14C above, a shorter length 388 will allow the filmstrip underneath the shield's minor width to receive some metal duringthe metallization process, thereby making it translucent. For example,if the length 308 of the embodiment in FIG. 9 is shortened, and itsmajor width 314 is less than the width of the film sheet beingmetallized, it will produce a film sheet with the followingcharacteristics, as depicted in FIG. 16: (a) one translucent strip 236having a width 228 approximately equal to the minor width 312 of theshield and having an approximately constant degree of transmittancethroughout its width 228; (b) two translucent strips 232, each having awidth 224 approximately equal to half the difference between the major314 and minor 312 widths of the shield 300, and each having a degree oftransmittance that varies along its width 224; and (c) two opaque strips230, each having a width 226 from the outer edge of the translucentstrip 232 to the corresponding edge of the film sheet.

FIG. 17A and 17B depict still another embodiment of the presentinvention. This shield in this embodiment comprises two plates 302, 304each with two faces and an edge, disposed adjacent to one another, faceto face. Furthermore, the plates are movably disposed such that one orboth plates are able to move in the lengthwise axial direction relativeto one another. Each plate is similar to the embodiment of FIG. 11,having saw teeth 330 along its length. In a first position, depicted inFIG. 17A, all of the saw teeth 330 on each plate are fully aligned withone another. When the shield is used in the first position, the width ofthe translucent strip of film will be approximately equal to the heightof the saw teeth 332, and the width of the transparent strip of filmwill be approximately equal to the minor width 312 of the shield. Asdescribed previously, the plates are movably disposed such that one orboth plates can be shifted in the direction of the plates' longitudinalaxes to a second position. In the second position, depicted in FIG. 17B,none of the saw teeth 330 on either plate are fully aligned with the sawteeth 330 of the other plate. In the second position, the minor width312 of the shield is increased, and the effective height 332 of the sawteeth is decreased. A sheet of film that is metallized using thisembodiment of the shield in the second position will have narrowertranslucent strips and a wider transparent strip, than a sheet of filmmetallized using this shield in the first position. In addition, whenthe shield is used in the second position the translucent strip willhave a more rapid change in transmittance across its width. Thisarrangement gives a practitioner of the present invention the ability tofinely tune the properties of the partially metallized film sheet, inthat the widths of the transparent strip and the translucent strips canbe changed to suit different applications without the need to replaceone shield with another.

FIGS. 18A, 18B and 18C depict another embodiment of the presentinvention. This shield in this embodiment comprises two plates, eachwith two faces and an edge, disposed adjacent to one another, face toface. Furthermore, the plates are movably disposed such that one or bothplates are able to move in the lengthwise axial direction relative toone another. Each plate is a solid plate that contains at least oneopening 390 comprising at least one target shape 398. The target shapecan be, for example, a product logo, as depicted in FIG. 18C, or agraphic design shape. The at least one target shape 398 is the same forboth plates. In a first position, depicted in FIG. 18B, the plates arearranged such that the at least one opening 390 in one plate is notaligned with the at least one opening 390 in the bottom plate.Therefore, in the first position, during metallization no vaporizedmetal 200 passes through the at least one opening 390 and the entirestrip of film beneath the shield remains transparent. In a secondposition, depicted in FIG. 18C, the plates are arranged such that the atleast one opening 390 in each plate is aligned with the other.Therefore, in the second position, during metallization vaporized metal200 is allowed to pass through the at least one opening and mark 394 thefilm with the target shape 398. During metallization, the plates areperiodically shifted from the first position to the second position andrapidly back to the first position. If the plates are left in the secondposition too long, the target shape 398 will bleed in the direction ofthe film's travel. In one embodiment, the partially metallized film willhave a transparent strip underneath the plates with periodic targetshapes 398 marked 394 within the transparent strip. In this embodiment,opaque strips will border the transparent strip. Also note that featuresof previously discussed embodiments, such as the saw teeth of the FIG.11 embodiment, or the trapezoid of FIG. 9, can be incorporated into thisembodiment to provide a gradual transition from opaque film totransparent film.

As stated previously, FIG. 10 depicts one embodiment of a partiallymetallized film sheet of the present invention with a gradual transitionfrom opaque film to transparent film, which is made using one embodimentof shield of the present invention. This partially metallized film stripcan, in turn, be used with the machine depicted in FIG. 3 to create amulti-layered packaging film sheet. FIG. 19 depicts a cross section ofone embodiment of a partially metallized, multi-layered packaging filmsheet utilizing one embodiment of a shield of the present invention andthe laminate machine depicted in FIG. 3. Most of the layers depictedtherein are similar to the prior art multi-layered packaging film sheet,except for the metallized layer 116 and the graphics layer 114. (Theimportance of the graphics layer will be discussed further below.) Ascan be seen, the thin metal layer 116 is dense nearer to the edges ofthe film sheet, which corresponds to the opaque strip discussedpreviously. The dense metal layer then gradually becomes less densetowards the center of the film sheet, which corresponds to thetranslucent strip discussed previously. The metal layer then disappearsaltogether near the center of the film sheet, which corresponds to thetransparent strip discussed previously.

As discussed previously, the transparent strip runs the entire length ofthe partially metallized film sheet. If no graphics layer 114 wereincluded in the multi-layered packaging film, the resulting packagewould have a transparent window that runs longitudinally along theentire length of the product package. A transparent product viewingwindow can thus be framed by carefully choosing the contents andplacement of the graphics layer. As depicted in FIG. 8, the graphicslayer can mask the transparent, translucent and opaque strips in atransverse direction across at least one area of the product package,thereby providing a transparent product viewing window in the unmaskedarea. The transparent product window on the food package is thus definedby at least one longitudinal opaque or translucent strips and at leastone transverse graphic strip, or, preferably, two transverse graphicstrips and/or product logos. Alternatively, a translucent window can beprovided as described previously. Foodstuffs inside the package can thenbe easily viewed by consumers through the window.

As used herein, the term “package” should be understood to include anycontainer including, but not limited to, any food container made up ofmulti-layer thin films. The partially metallized film described hereinis particularly suitable for forming packages for snack foods such aspotato chips, corn chips, tortilla chips and the like. However, whilethe layers and films discussed herein are contemplated for use inprocesses for the packaging of snack foods, such as the filling andsealing of bags of snack foods, the layers and films can also be put touse in processes for the packaging of other low moisture products.

Product packages made using partially metallized films, whereinapproximately 80% of the area of the film used in the package wasmetallized, resulted in vastly improved barrier properties overunmetallized films. For example, in one embodiment of a packageutilizing such partially metallized film, moisture vapor transmissionrates were reduced by about 68% below the MVTR for the same size packagecreated using unmetallized film. In another embodiment of a packageutilizing such partially metallized film, the oxygen transmission ratethrough the package walls was reduced by about 80% below the OTR for thesame size package created using unmetallized film. In anotherembodiment, a package utilizing such partially metallized film andcontaining 13 ounces of tortilla chips was able to maintain productfreshness (less than 2% product moisture, by weight) for more than eightweeks, whereas a package made using unmetallized film kept the productfresh for less than two weeks.

While this invention has been particularly shown and described withreference to a preferred embodiment, it will be understood by thoseskilled in the art that various changes in form and detail may be madetherein without departing from the spirit and scope of the invention.

What is claimed is:
 1. A food package made from a partially metallizedpackaging film comprising: product viewing window comprising a sectionof transparent packaging film and defined by at least one translucentfilm strip or at least one opaque film strip, and at least one productpackage graphic.
 2. The food package of claim 1 wherein said translucentfilm strip comprises an outer edge, an inner edge, and a width generallyrunning between said outer and inner edges, and a degree oftransmittance that varies across its width.
 3. The food package of claim1 wherein said degree of transmittance varies linearly across its width.4. The food package of claim 1 wherein said product viewing window isfurther defined by two translucent film strips on opposite sides of saidproduct viewing window, and two package graphics on opposite sides ofsaid product viewing window.
 5. The food package of claim 1 furthercomprising at least one metallized target shape on said section oftransparent packaging film.
 6. A method of making a partially metallizedpackaging film comprising: providing a vaporized metal stream and asheet of packaging film; moving said sheet of packaging film throughsaid vaporized metal stream; during said moving, shielding at least oneportion of said vaporized metal stream from contacting said packagingfilm.
 7. The method of claim 6 further wherein said shielding furthercomprises disposing a shield between said vaporized metal stream andsaid sheet of packaging film without allowing said shield to contactsaid packaging film.
 8. The method of claim 7 wherein said shieldingfurther comprises intermittently allowing at least one portion of saidvaporized metal stream to contact said sheet in at least one productlogo shape.
 9. The method of claim 7 wherein said disposing said shieldfurther comprises disposing a rigid plate.
 10. An apparatus for creatinga partially metallized packaging film comprising: a vaporized metalsprayer that produces a vaporized metal stream; a shield disposed withinthe vaporized metal stream such that any packaging film sheet used withthe apparatus will have at least one portion of the vaporized metalstream shielded from contacting it.
 11. The apparatus of claim 10wherein said shield is disposed such that it does not touch anypackaging film sheet used with the apparatus.
 12. The apparatus of claim10 wherein said shield further comprises a rigid plate.
 13. Theapparatus of claim 12 wherein said shield further comprises a length, amajor width, and a minor width.
 14. The apparatus of claim 10 whereinsaid shield is disposed generally co-planar with any packaging filmsheet used with the apparatus.
 15. The apparatus of claim 13 whereinsaid shield further comprises a transition from said major width to saidminor width comprising at least one of, a linear transition, a concavetransition, a convex transition, a stepped transition and a saw toothtransition.